diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..d86f343
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,3 @@
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+pythonpath = ["lambdas/classifier", "lambdas/slack_post", "cdk"]
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..90357e0
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,13 @@
+"""Central test configuration.
+
+Sets dummy environment variables at import time so modules that read
+``os.environ`` at module load (slackio, interactions, handler) can be imported
+without real AWS credentials.  Real values are monkeypatched per-test where
+needed.
+"""
+
+import os
+
+os.environ.setdefault("SLACK_SECRET_NAME", "test-slack-secret")
+os.environ.setdefault("DASHBOARD_URL_PARAM", "/test/dashboard-url")
+os.environ.setdefault("ANALYTICS_BUCKET", "test-bucket")